Real Time Kinetic mobile machine control [Professional]

Introduction

Real Time Kinematic (RTK) mobile machine control requires a sufficient number of global positioning system (GPS) satellites that are both visible and suitably positioned.

Reliably obtaining the highest degree of accuracy afforded by RTK technology requires the initial acquiring of a solution, the maintaining and if it is lost, rapidly reestablishing the RTK fix solution. Losing the RTK fix solution is a common occurrence when operating near trees, tall landforms, and large structures that can cause significant sky blockage. Operators can increase the likelihood of acquiring and maintaining an RTK fix solution by incorporating more satellites from multi-national Global Navigation Satellite System (GNSS) constellations.

However, this added capability is only of practical economic benefit when and if operating near sky blockages. Due to the additional expense in upgrading mobile machine control to full GNSS coverage capabilities, upgrade considerations should include the impact of sky blockages surrounding production fields caused by the rolling terrain, nearby landforms, and most importantly, field-surrounding tree canopies. ^[1]

Αποτέλεσμα εικόνας για rtk gps — Figure 1: RTK GPS Explained.^[2]

The simplest and cheapest method is to use an RTK GPS receiver is to receive real-time corrections from an RTK Network of base stations. These networks for RTK are typically run by state Departments of Transportation, but there are also many private pay-for-service networks around the U.S. Access to the Network is free in many areas and Anatum can help you determine availability in your area. The method employed by this technology using an RTK Network looks like the image below.

Bluetooth RTK receiver models, like the Eos Arrow Gold RTK, Arrow Gold Basic, and Arrow 200 RTK ^[3] have made it increasingly easier for biologists, geologists, engineers, and other workers traditionally using sub-meter workflows to acquire reliable centimeter-grade location data.

Sure, most people from those career fields would look at a centimeter RTK receiver and say it is overkill because their accuracy requirement is only sub-meter. A sub-meter GNSS receiver is certainly a valid option, and you can see that receivers like the Arrow 100 and iSXBlue II performed quite well in our field test comparison. But what if you could buy or rent a centimeter RTK Arrow 200 receiver for the same price you currently pay for that standard handheld GNSS unit that doesn’t Bluetooth to your field tablet and only gets <1m accuracy real-time with SBAS (WAAS) corrections? And with that handheld, if you want <50cm accuracy you will have to collect extra data in the field and complete time-consuming post-processing analyses to get your field data that accurate.

Transitioning away from that handheld GNSS unit to a Bluetooth RTK receiver and tablet will:

Give your field teams increased confidence they are getting their required accuracy in real-time
Provide your GIS staff with a simpler workflow since all location, photographic, and asset data will come from the tablet
Eliminate the need for time-consuming post-processing of location data
Provide the project manager with more accurate data and project cost savings to better compete on job proposals

For consulting firms with clients that require post-processing, utilizing a Bluetooth RTK receiver can eliminate that requirement through an information sharing discussion with your client. Essentially, the same types of calculations done with the post-processing method to increase the accuracy of field location data is being done in real-time by RTK base station networks if your RTK receiver is connected through cellular service to your local RTK network. The RTK network is pulling the same satellite data used in post-processing and conducting corrections analyses, and then broadcasting those corrections from an NTRIP Castor live right to your Bluetooth RTK receiver connected to your field tablet! The project savings over legacy post-processing methods are truly significant.

Figure 2: Galileo constellation and occupation status of orbital slots.

For the four-system combination GGGB, Figure 3 shows the satellite usage for each individual system over the two-day period. It can be seen that for a short baseline of 2 km, a maximum number of four Galileo satellites can be used for positioning. In fact, during 80.3% of the whole test period, the number of Galileo satellites used in RTK fixed solutions is equal to or greater than the number of BeiDou satellites used.

Figure 3: Number of satellites used in RTK fixed positions with GGGB under open sky.

In terms of positioning accuracy, Figure 4 compares the 3D errors from analyzing the long baseline data with different GNSS constellations. Regarding the entire two-day period illustrated in Figure 3a, the integration of BeiDou (GG vs. GGB) and Galileo (GGB vs. GGGB) results in higher position repeatability with more consistent errors. For a selected period of 12 hours, Figure 3b highlights the advantages of Galileo in reducing large 3D errors from 6–8 cm to 3–4 cm, where two or three Galileo satellites are used in case of GGGB.